1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
There is known an image forming apparatus having a unit that releases pressure-contact of a fixing member in conjunction with an opening action of an opening/closing cover of the image forming apparatus and allows for the pressure-contact of the fixing member in conjunction with a closing action of the opening/closing cover (see Japanese Patent Application Laid-Open No. 2005-077615). In the case where a recording sheet is jammed at a fixing nip portion, when the opening/closing cover is opened, a pressing state of the fixing nip portion is released. Therefore, there are the advantages that no motor is needed for releasing the pressure to reduce the cost, and that the release of pressure can be performed easily.
There are some image forming apparatuses in the market, in which an apparatus main body is set to have a longer life than a fixing unit. In such apparatus, the fixing unit can be exchanged.
In the above-mentioned apparatus in which the pressing state of the fixing nip portion is released in conjunction with the opening action of the opening/closing cover, if the fixing unit is exchangeable, the following problem occurs. FIGS. 8A to 8E are schematic views illustrating a mounting action of the fixing unit in the image forming apparatus.
In FIGS. 8A to 8E, a coupling 61, as an interlocking member that works in conjunction with the opening/closing cover, is disposed in the main body of the image forming apparatus, and a cam member 62, as a pressure-releasing member, is disposed in a fixing unit T. A fixing nip portion N is pressed (FIG. 8E), or the pressure thereof is released or reduced (FIG. 8A), by rotation of the cam member 62.
The coupling 61 works in conjunction with the opening action of the opening/closing cover (not shown) disposed in the main body of the image forming apparatus, and rotates from a position of FIG. 8E in the clockwise direction in FIG. 8E to a position of FIG. 8A. In conjunction with rotation of the coupling 61, the cam member 62 rotates so as to release or reduce the pressure to the fixing nip portion N. As illustrated in FIG. 8B, in the state where the pressure to the fixing nip portion N is released or reduced, the fixing unit T can be mounted to or detached from the image forming apparatus in the left direction of FIG. 8B.
While a user is detaching the fixing unit T from the image forming apparatus (FIG. 8B) and performing a jam recovery or the like, the user may touch the cam member 62 unintentionally so that the cam member 62 rotates by a rotation angle other than the angle for releasing pressure of the fixing member. If a phase shift between the cam member 62 and the coupling 61 occurs (FIG. 8C), a rib 62a of the cam member 62 for rotating the cam member 62 cannot be inserted into the coupling 61 (FIG. 8D). Then, the fixing unit T cannot be mounted to the image forming apparatus.